Position Control of Parallel Active Link Suspension With Backlash

In this article, a position control scheme for the novel parallel active link suspension (PALS) with backlash is developed to enhance the vehicle ride comfort and road holding. A PALS-retrofitted quarter car test rig is adopted, with the torque flow and backlash effect on the suspension performance is analyzed. An elastic linear equivalent model of the PALS-retrofitted quarter car, which bridges the actuator position and the equivalent force between the sprung and unsprung masses, is proposed and mathematically derived, with both the geometry and backlash nonlinearities compensated. A position control scheme is then synthesized, with an outer loop H$_{\infty}$ control for ride comfort and road holding enhancement and an inner loop cascaded proportional-integral control for the reference position tracking. Experiments with the PALS-retrofitted quarter car test rig are performed over road cases of a harmonic road, a smoothed bump, and frequency swept road excitation. As compared to a conventional torque control scheme, the newly proposed position control maintains the performance enhancement by the PALS, while it notably attenuates the overshoot in the actuator's speed variation, and thereby it benefits the PALS with less power demand and less suspension deflection increment.